1. Field of the Invention
The present invention relates to a vibratory gyroscope, and particularly to a vibratory gyroscope applicable in, for example, a navigation system which detects an angular velocity to detect a position of a moving object for proper guidance, or a yaw rate sensor which detects an external vibration for proper damping and the like.
2. Description of the Prior Art
FIG. 5 is a perspective view showing an example of a conventional vibratory gyroscope serving as a background of the present invention, and FIG. 6 is its side view. The vibratory gyroscope 1 includes a vibrating body 2. On side faces of the vibrating body 2, piezoelectric elements 3a, 3b and 3c are formed respectively. The piezoelectric elements 3a, 3b and 3c are formed with electrodes on both surfaces of piezoelectric ceramics. The piezoelectric elements 3a, 3b and 3c are bonded in the side faces of the vibrating body 2 by means of soldering, conductive adhesives or the like. To the piezoelectric elements 3a, 3b and 3c, lead wires 4a, 4b and 4c are connected to the vicinity of nodal points of the vibrating body 2 by means of bonding or soldering. The lead wires 4a, 4b and 4c are used for inputting and outputting the signals to and from the piezoelectric elements 3a, 3b and 3c. The reason for connecting the lead wires 4a, 4b and 4c in the vicinity of the nodal points of the vibrating body 2 is for preventing the characteristic deterioration of the vibratory gyroscope 1 due to the leakage of vibration of the vibrating body 2 through the lead wires.
The vibrating body 2 is supported by support members 5 at ridge portions in the vicinity of its nodal points, and the support members 5 are fixed to a support base 6. In order to minimize a thermal stress at the time of bonding the piezoelectric elements 3a, 3b and 3c to the side faces of the vibrating body 2, and a stress exerted on the piezoelectric elements 3a, 3b and 3c by changes in atmospheric temperature, a thermal expansion coefficient of the vibrating body 2 and that of the piezoelectric elements 3a, 3b and 3c must be coincided. Hence, for example, a Ni--Fe alloy having the thermal expansion coefficient close to that of the piezoelectric ceramics is used as a material of the vibrating body 2.
In the vibratory gyroscope 1, between the piezoelectric elements 3a, 3b and the piezoelectric element 3c, an oscillation circuit and the like is connected as a feedback loop for self-oscillation drive. The vibrating body 2 is bent and vibrated in a direction perpendicular to a surface of the piezoelectric element 3c by a driving signal from the oscillation circuit. When the vibratory gyroscope is rotated about an axis of the vibrating body 2 in this state, the vibrating direction of the vibrating body 2 is changed by a Coriolis force, and the output difference is produced between the piezoelectric elements 3a and 3b. A rotational angular velocity can be detected by measuring the output difference. In this vibratory gyroscope 1, the ridge portion of the vibrating body 2 is cut to adjust the frequency and sensitivity.
In such a vibratory gyroscope, since the lead wires 4a-4c are connected in the vicinity of the nodal points of the vibrating body 2, the piezoelectric elements 3a-3c must be formed into the size including the vicinity of the nodal points of the vibrating body 2. However, generally, the piezoelectric ceramics used in the piezoelectric elements 3a-3c has a low Q (i.e. quality factor). Hence, when the piezoelectric elements 3a-3c are large, even when a material having the high Q (i.e. quality factor) is used as the material of the vibrating body 2, Q is low as the entire vibratory gyroscope.
When metallic materials are used as the material of the vibrating body 2, when the ridge portion of the vibrating body 2 is cut to adjust the frequency and sensitivity of the vibratory gyroscope 1, a burr 7 as shown in FIG. 7 is produced by a ductility of the metal. When such a burr 7 is produced, a plurality of characteristics of the vibratory gyroscope 1 become unstable.